Cardiac leads may be endocardial leads, such as leads for sensing/pacing in right heart cavities, or leads introduced in the coronary network, notably leads comprising an electrode positioned in front of a left cavity of the myocardium.
The insertion of the latter type of leads, carried out through endocavitary approaches, is a particularly tricky intervention, taking into account the difficult access to the coronary sinus entrance via the right atrium, and also the required accuracy for the pacing sites once the lead is guided to its desired position and immobilized within the coronary network.
One of the implantation techniques of such a lead requires an accessory known as “guide-catheter”. This accessory comprises a hollow tubular sheath reinforced by a wire mesh and with an inner surface presenting a low coefficient of friction (for example, a surface made with PTFE, extruded or co-molded with the rest of the sheath). In addition, the sheath is designed to present a flexibility allowing a stiffness in torsion high enough to allow transmission of a rotation movement from one end to the other, so as to allow guiding the lead tip within the myocardium during the procedure.
Once in place, the guide-catheter serves as a direct “tunnel” between the “external world” and the coronary sinus, a tunnel that can be utilized by the surgeon for sliding the lead through up to its final target site.
Once the lead is in place, the guide-catheter needs to be extracted, and the extraction procedure is tricky because the lead must not be displaced, or its position or orientation altered as a result of the extraction.
These catheters also need to have a minimum diameter so as to allow their navigating through blood vessels while being less traumatic and more easily guidable. Also, the catheter dimensions are adjusted to the lead for a better performance.
One other difficulty of this extraction step is due to the presence of the electrical connector, at the proximal end of the lead. The diameter of this connector is greater than that of the internal lumen of the guide-catheter, and it prevents the guide-catheter from being withdrawn by being simply slid backwardly along the lead.
The step of extracting the guide-catheter therefore usually requires it to be cut, starting from its proximal end and along a generatrix line by means of a slitting tool, also known as “slitter”, for slitting the proximal end of the catheter and reinforcement wire mesh forming the frame of the hollow sheath.
With one hand, the surgeon then pulls the guide catheter towards him with a continuous gesture, while firmly maintaining the lead and the slitting tool with the other hand, allowing the slitting tool to simultaneously slit the sheath as it is being thus extracted.
It has already been proposed in the prior art, in order to avoid resorting to a sharp cutting tool, to use a non-reinforced sheath that is simply strippable. However, cutting of such a sheath along its whole length leads to a weakness and a lower rigidity of the guide-catheter, with a risk of folding and lower transmission of efforts (applied forces) during its setting up preparatory to an intervention event. It has also been proposed, notably by European patent EP 1,155,710 and its U.S. counterpart U.S. Pat. No. 6,625,496 (commonly assigned herewith to ELA Medical), to provide the lead with a removable connector, which avoids having to cut the guide-catheter. This method however leads to an increasing number of steps required for setting up and assembling the different elements, and also renders the intervention procedure more complicated.
Therefore, slitting/cutting of the guide-catheter is, in practice, the most usual way to proceed.
One of the main difficulties inherent to this method, lies in the risk of a lead displacement during the catheter extraction. In such case, it is necessary to completely remove the lead and start over again, from the very beginning, the procedure of insertion and placement of the lead. This implies a significantly longer intervention time, particularly with left ventricular leads, which take a very long time to implant anyway, and additional risks associated with the prolongation of an already very long intervention.
Some slitting tool configurations have for example been proposed in U.S. Pat. Nos. 4,687,469 (Osypka), 4,997,424 (Little), 6,159,198 (Gardeski), 5,330,460 (Moss) and 7,029,460 (Gardeski). The devices described in these patents propose various ways of maintaining the lead during the procedure of cutting the guide-catheter, and protecting the lead from being damaged by the blade during this operation.
U.S. patent application 2007/0079511, describes a cutting tool having a blade holder with a flattened shape to be held between two fingers (thumb and forefinger). This blade holder comprises, in its rear area, a footprint for the thumb, which is crossed by a curved pathway located in the continuation of a tubular element receiving and guiding the lead in the vicinity of the blade during the cutting of the guide-catheter sheath.
In concrete terms, the devices heretofore proposed in the prior art all present certain drawbacks.
In particular, the risk referred to above, which is a large risk, of a lead displacement during the cutting operation, is increased by the fact that the lead is not maintained in the critical area of cutting of the catheter, an area where the constraint during the operation, is focused. For that reason, there is a remaining risk of a displacement of the lead relative to the catheter, with the formation of a “loop” level with the maintaining area, leading to a high risk of displacement of the opposite end (distal end) located level with the implantation site, such a displacement requiring a complete starting over of the procedure.
Also, with the slitting tools that have been proposed so far, the prehension of the tool is ensured by a pinching between the thumb and forefinger, with a risk of instability during handling that is as much high as the required cutting force is high, notably in the case of relatively thick and strongly reinforced guide-catheters.
As for the prehension of the lead, it is equally ensured by the fingers, but at a relatively large distance from the area where the cutting of the guide-catheter is effectively realized, which reduces the stability of the whole assembly set up during the operation.
To summarize, the slitting tools that have been proposed so far always require a very accurate dexterity and a great experience of the surgeon so as to avoid any mishandling that would be disastrous.